Tile Talk: Alternative Roof Cladding Options

Structural Considerations For Reroofing Opens New Markets

by Richard K. Olson, president & technical director, Tile Roofing Industry Alliance

(Editor’s Note:  Richard K. Olson is president and technical director for the Tile Roofing Industry Alliance.  The association represents industry professionals involved in the manufacturing and installation of concrete and clay tile roofs in the United States and Canada, and works with national, state, and local building officials to develop installation techniques, codes, and standards for better roofing systems.  Olson can be reached at rolson@tileroofing.org.)

In today’s roofing market, consumers are pursuing alternative roof cladding options for their reroofing projects on existing buildings.  The desire to increase energy efficiency, long-term performance, and the reduction of life cycle costs are driving these decisions.  This will create new opportunities to help determine the structural fundamentals for achieving these demands.  These decisions are driving the reroof market from the traditional two-tab of past, to upgraded systems like concrete and clay roof tiles.  While slightly heavier than existing shingles, there are easy and inexpensive revisions that can be made when a structure might need additional support. 

         Design professionals can easily assess the existing roof structure to determine needs.  The first step will be to perform an inspection for the existing structure that should include the details of the full load path.  For steep-slope applications, we can generally do inspections via the attic for proper identification of the existing roof support system.  Be sure to note the lumber species, rafter size, and spacing, including the spans for supports.  Note the design, spacing, and species of any purlins, struts, and collar ties.  Identify the load-bearing walls and connections to the roof, wall, and foundations.  During inspection, evaluate the condition of the current rafters for any repairs that may be required during reroof activities.  These can be called out in plans as repair items. 

         Once you have gathered the information, review the local building code requirements to identify established live and dead load values that have been formally adopted for designing a roof assembly.  In addition, most jurisdictions will have best practices they recommend, and these will need to be incorporated into the reroof designs.  These will provide the live load, dead load, roof sheathing, and roof framing that incorporate the weight considerations for the desired roof cladding.  All steep-slope roof claddings will have the same required design live, sheathing, and roof framing load.  The actual increase in weight of the overall roof load between options is only a portion of the overall design identified for the roof cladding, as the other items are required.  Therefore, many existing roofs can already handle the roof cladding options being considered.

         Then, determine the additional structural support, if any, that might need to be accounted for.  The American Wood Council has printed span charts and calculators readily available to assist in the determination of the maximum spans allowed for the rafter designs.  By reviewing the information you have captured during your inspection, you can quickly determine the required roof structural support you will need.  

         Items that you might give call out details for could include: identification of the plot load path that transfers the roof loads downward to foundation by means of conventional framing methods; identification of load bearing points that allow the roof load to be supported to bearing walls or support beams; design modifications to help strengthen rafters or reduce spans to prevent over spanning the rafter system, including additional struts, purlins, or collar ties; consider any upgrade of tie systems as rafters ties triangulate the rafter system and prevent spreading/outward force; and consider enhancing connections to comply with code requirements, and make sure to address necessary repairs as split wood must be repaired or replaced.

         As an industry association the Tile Roofing Industry Alliance has developed and made available short courses on how to deal with structural issues surrounding a roofs structural needs for reroof applications.  In a condensed format, we can provide training to you or your staff on how the above items can be used to easily and cost-effectively design any roof to handle concrete and clay roofing tiles.  Having this information and a greater understanding for how to create cost-effective designs will be a value-added proposition for selling your services to the building owner or roofing professional.  In addition, it will open the opportunities for creating a more aesthetic-looking roof design that roofing market trends are moving towards.  This is a great time to take opportunities for additional training to help grow your business.

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